1. Field of the Invention
The invention relates generally to the art of temperature warning systems for vehicles, and in particular to temperature warning systems for the non-drive axles of heavy-duty vehicles, such as tractor-trailers or semi-trailers, and straight trucks, which are capable of functioning during vehicle operation. More particularly, the invention relates to a vehicle temperature warning system which utilizes a thermal plug that includes a fusible material and which is located in or adjacent to the wheel end assembly of a heavy-duty vehicle. The thermal plug operates in conjunction with a pressurized air supply and a flow sensor to alert the driver of the vehicle of an undesirable temperature condition in the wheel end assembly and/or the axle spindle end during operation of the vehicle.
2. Description of Related Art
Reference herein is made to tractor-trailers and semi-trailers by way of example, with the understanding that such reference applies to other heavy-duty vehicles, such as straight trucks. All tractor-trailers include at least one trailer, and sometimes two or three trailers, all of which are pulled by a single tractor. Each trailer includes a frame, from which at least one axle is suspended. A wheel end assembly is rotatably mounted on each end of the axle. More specifically, each wheel end assembly includes bearing assemblies that are mounted on a respective axle spindle end and a wheel hub which in turn is mounted on the bearing assemblies. In this manner, the bearing assemblies enable the wheel hub to rotate about the axle spindle end. A wheel rim including a tire is, in turn, mounted on the wheel hub in a manner well known to those having skill in the art.
To facilitate smooth rotation of each wheel hub about its respective axle spindle end, the bearing assemblies typically include lubricant. A bearing assembly seal formed of a relatively flexible material, such as rubber, is disposed on the inboard end of the wheel hub to isolate the bearing assemblies in order to prevent contaminants from passing into the bearing assemblies, and to contain the lubricant within the bearing assemblies. Repeated excessive speed or excessive braking of the vehicle often generates a large amount of heat in components of the wheel end assembly and/or the axle spindle end, in turn heating the bearing assembly lubricant and/or the bearing assembly seal, which may cause degradation of the lubricant and/or the seal. If the lubricant degrades, rotation of the wheel hub about the axle spindle end may become impaired and can result in damage to or failure of the wheel end assembly and/or the axle spindle end.
Alternatively, if the seal degrades, the lubricant may escape, or external contaminants may pass into the bearing assemblies, which can impair the rotation of the wheel hub about the axle spindle end and may potentially damage the wheel end assembly and/or the axle spindle end. It is this impaired rotation of the wheel end assembly about the axle spindle end that produces excessive heat in the wheel end assembly and in the axle spindle end. Similar potential damage may be caused by installation problems which can detrimentally affect the lubricant and/or bearing assemblies, and thus allow excessive heat to be generated in the wheel end assembly components and/or the axle spindle end. Such installation problems include situations in which the lubricant accidentally may have been omitted from the bearing assemblies, and/or over-tightening of the bearing assembly retaining nuts, which can overload the bearing assemblies. Moreover, absent the problem conditions set forth above, it is well documented and known to those having ordinary skill in the art that the bearing assemblies themselves typically exhibit excessive heat prior to failure.
In addition, in some applications, sealed bearing assemblies are used. Sealed bearing assemblies are self-contained units that are packed with lubricant and include a seal that is built into the bearing assembly. Such sealed bearing assemblies are known in the art as being non-serviceable, and thus typically cannot readily be opened in order to replace or add lubricant if the lubricant escapes the assembly or degrades. Rather, sealed bearing assemblies are typically removed from service and replaced if such a problem does occur. Since it is desirable to remove a sealed bearing assembly from service in the event that such a problem does occur, it is advantageous to attempt to monitor conditions that may indicate a potential problem, such as the generation of excessive heat, as described above.
Because multiple trailers, each possibly having multiple axles and multiple wheel end assemblies, may be pulled by a single tractor, the chance that a given wheel end assembly and/or axle spindle end may become impaired from the above-described conditions without detection by the vehicle operator increases. Because the potential damage resulting from such impairment is undesirable, it is advantageous to attempt to monitor the components of the axle, including the axle spindle ends and/or the wheel end assemblies, for high-temperature conditions. Such conditions may indicate degradation of or a lack of the proper amount of lubricant in the bearing assemblies, degradation of the bearing assembly seals, contamination in the bearing assemblies, an overloading of the bearing assemblies, or the breakdown of the bearing assembly itself. It is also advantageous to alert the operator to remove the vehicle from service to reduce the potential damage that may result from such conditions.
Prior art approaches to monitor conditions at the wheel end assembly typically utilize a programmable microprocessor to control the monitoring system. These approaches typically include a monitoring device for detecting problem conditions at the wheel end assemblies, which device typically includes a sensor located on the axle within the wheel hub, a microprocessor for receiving and processing the signals from the sensor to detect a problem condition at the wheel end assembly, and an indicator means to alert the driver of the problem condition. More particularly, the microprocessor interprets incoming data signals from the sensor disposed on the axle within the wheel hub and executes a pre-programmed decision-making process to determine when an alarm should be activated. These systems typically require complex wiring systems that make them costly to manufacture and difficult to install on the vehicle. Moreover, these systems also include thermal sensors which are relatively fragile and which are located within the axle spindle end of the axle which makes them difficult to replace when they become damaged or simply wear out due to normal wear and tear on the system.
Still other prior art temperature warning systems have incorporated wireless systems utilizing radio frequency transmitters and receivers in order to eliminate the need for the heretofore noted complex wiring systems. However, these systems also have demonstrated potential problems in that interference between the transmitter and the receiver can cause false indications of a problem condition when no problem condition actually exists.
Still other prior art temperature warning systems have included sensors which utilize fusible materials for sensing excessive heat conditions. However, those systems have located the fusible material within the axle spindle end which, when activated by exposure to an excessive heat condition, can release contaminants, i.e., the melted fusible material, into the wheel end assembly, and/or cause pressure to build in the wheel end assembly which can potentially cause the bearing assembly seal to leak, which in turn can potentially cause premature failure of the bearing assemblies.
Thus, a need exists in the art for a vehicle temperature warning system that: eliminates the need for relatively fragile thermal sensors which can potentially become damaged or wear out; which is better able to detect excessive heat in the axle spindle end and/or the wheel end assembly because of its position adjacent the bearing assemblies; which avoids contamination and pressure build-up in the wheel end assembly; and which is easily accessible for both replacement and/or maintenance of the system, yet still remains simple, reliable and cost efficient as compared to prior art temperature warning systems.